The synthesis of gold nanoparticles has been shown to take place via the reduction of HAuCl4 in the presence of alkanethiols.1-5 Recently, there have been an increasing number of reports on the preparation and utilization of such thiol-stabilised gold nanoparticles; often referred to as monolayer-protected clusters (MPC).6 Potential applications of these types of systems include optical devices, microelectronics, catalysis and chemical recognition.7-9 In this regard, a great deal of attention is now focused on the functionalisation of the stabilising ligands.10-12 
Phthalocyanines (Pcs) have been shown to have potential applications in the areas of electrophotography13, chemical sensors14, photovoltaic cells15 and as second generation photosensitisers in the anti-cancer modality termed photodynamic therapy (PDT).16,17 
Other photosensitiser materials are known as such. For example, porphyrins can act as a photosensitiser.
Of the many prospective uses of photosensitisers such as phthalocyanines or porphyrins, we are interested in the potential of these macrocyclic compounds in the field of PDT.18,19 PDT involves the selective bio-distribution of a suitably designed photosensitiser molecule near to or within a cell to be killed. Once located, the photosensitiser is excited using light. Excited state energy is then transferred from the triplet state of the sensitiser to the ground state of molecular oxygen producing the cytotoxic species singlet oxygen (1O2).20 The generation of the latter species is the principal target for the present invention.
Cancerous cells are just one possible application for this technology. The formation of singlet oxygen will initiate the destruction of a multitude of disease inducing or diseased cells, or indeed bacteria or viruses. The mode of cell kill is due to the highly oxidising nature of singlet oxygen. A photosensitiser can be defined as “a molecule which when excited by light (usually visible although possibly ultraviolet or near infrared) produces a reactive oxygen species, either singlet oxygen or an oxygen free radical, which is cytotoxic”.
Previously we have reported the self-assembly of Pc molecules on 2D planar gold films, with attachment of the macrocyclic ring via a mercaptoalkyl tether.21 